Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 200855
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
255 AM CST Tue Feb 20 2018

.SHORT TERM...(Today through Thursday night)
Issued at 255 AM CST Tue Feb 20 2018

Unseasonably mild conditions prevail early this morning with
temperatures in the mid 60s to around 70, along with south winds 10
to 20 mph with gusts to 30+ mph. A few showers were seen moving
toward SEMO. Best PoPs will remain across the NW 1/3 of the CWFA
today, and in fact may retreat farther NW with time as the overall
precipitation area becomes more aligned with an approaching cold
front, that should be just off to our NW from around KSTL to KUNO
around 6 p.m. Otherwise, another unseasonably warm day with right at
record temperatures forecast. It will be quite breezy again, but
remain mostly below Advisory levels. Tonight, through midnight,
PoPs will focus across the NW 1/2 of the area, while remaining
essentially dry across the KY Pennyrile. After midnight, as the
front progresses east across the area, showers and a few
thunderstorms will accompany the front and continue behind it. As
we said yesterday, the axis of activity will be closely aligned
with the 850mb front. For today through tonight, a general model
consensus was used, with a respectable incorporation of what the
CAM`s showed.

It will be noticeably cooler Wednesday in the wake of the surface
front. However, rain showers will continue. For Wednesday through
Thursday night, we moved away from the GFS, and went with the wetter
NAM, ECMWF, CMC solutions. The GFS continues to want to push
moisture to our south and east faster through Wednesday night, which
doesn`t seem as plausible given the strong 700mb and above SW mid
tropospheric flow. We do think there will be a let up in the
activity Thursday from NW to SE, save for the KY/TN state line
area into the KY Pennyrile. Thursday night, showers and a few
storms will surge back NE across most of the area. Thus our PoPs
and QPF will be a bit higher then blends and the GFS, which is
essentially what we did yesterday.

It is still too soon to hoist a Flood Watch. But, one will
eventually be needed. The latest soil moisture anomalies for our
area show mostly drier than normal conditions, near normal KY
Pennyrile. This along with 3-4.5 24hr FFG values both suggest we
can handle the initial stage setting rains. The concern for areal
flooding will increase with time mid to late week as ground
conditions become more saturated. That`s not to say we won`t see
isolated issues before then. We`ll continue with the ESF. If QPF
forecasts trend up, then a watch may be needed a little sooner.
High efficieny rains anticipated with PW`s 2+SD`s above the norm.
Integrated Water Vapor Transport (IVT) forecasts off the NAM are
impressive as well. It does show a slight SE shift and weakening
with time especially by late Wednesday night into Thursday,
picking back up again Thursday night. Temperatures will rebound
Thursday and Thursday night as well as return flow develops.

.LONG TERM...(Friday through Monday)
Issued at 255 AM CST Tue Feb 20 2018

The primary concern in the long term is the potential for heavy
rainfall and flooding Friday into Saturday night. While finer
details such as precipitation amounts and the axis of heaviest rain
still need some fine tuning, overall forecast confidence is higher
than average given generally good agreement among forecast models.

An anomalously moist southwest flow pattern will continue into the
first half of the long term period. Perturbations in the strong
southwest flow pattern will provide the necessary lift to generate
no fewer than three precipitation events during the period. The
first round of rain is expected to continue from Thursday night into
Friday as energy ripples along a stalled out frontal boundary draped
southwest to northeast across the area. The second round of rain
will likely arrive Friday night into early Saturday as a warm front
lifts north across the area. The third and final round of activity
should accompany the approach and passage of a cold front late
Saturday afternoon into Saturday night.

Some of the rain that falls could be quite heavy with precipitable
water values forecast to be 2 to 3 standard deviations above normal.
Per the collaborated forecast grids and WPC Days 4-5 QPF, rainfall
totals of 2 to 4 inches are possible over much of the area. That`s
in addition to what occurs prior to Friday. Thunder will also be
possible through much of the period, which will serve to focus even
heavier rainfall amounts in some basins--leading to the potential
for flash flooding.

We will also need to monitor the potential of severe weather--mainly
Saturday afternoon into Saturday night--as deep layer shear combines
with what could be respectable surface-based instability south of
the surface low. More uncertain will be the quality of surface-based
instability given the amount of sky cover and rain forecast.

The precipitation should taper off from west to east Saturday night
as the cold front sweeps through. In its wake, dry and slightly
cooler conditions are forecast to start the new week as high
pressure builds in. After unseasonably warm conditions Friday and
Saturday, a return to temperatures still slightly above normal is
forecast Sunday and Monday. Generally used a blend of available
guidance for temperatures, though readings could be several degrees
warmer than forecast Friday and especially Saturday if the 20/00Z
GFS MOS pans out.

&&

.AVIATION...
Issued at 433 PM CST Mon Feb 19 2018

Satellite reveals a few lingering bases in the MVFR range, but
mostly, VFR base clouds/cigs, and we anticipate that to continue
into/thru the first half of the night. Bases will lower later
tonight/toward morning, with rain chances incoming from the west,
so we reintroduce MVFR cigs for that time range, keeping vsbys vfr
even with chance/showers. Gusty southerlies will pick up again
tmrw.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$



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